The present invention relates to the peak detection and peak sense detection or phase discrimination of a reproducing signal in a system for reproducing a magnetic record on a medium such as a magnetic tape, a magnetic disk, or the like. In particular, it relates to a peak detection system for reducing intersymbol interference (ISI) in code signals to thereby improve the S/N of a reproducing signal.
Maximum-likelihood peak position detection techniques applied to peak detection to equivalently reduce noise have been discussed in: H. Burkhardt, "An Event-driven Maximum-likelihood Peak Position Detector for Run-length-limited Codes in Magnetic Recording", IEEE Transactions on Magnetics, Vol. MAG-17, No. 6, pp. 3337-3339 (1981), and in U.S. Pat. No. 4,644,564.
Digital magnetic recording and signal processing techniques have been discussed in F. Dolivo, "Signal Processing for High-Density Digital Magnetic Recording", IEEE, pp. 1-91-96 (1989).
When magnetic recording is applied to a medium 31 in FIG. 1A, recording bits 30 composed of "1" and "0" (see FIG. 1B) are recorded as the presence and absence of magnetic flux change on the medium 31. Any one of MFM or run-length-limited codes such as (1, 7) code and (2, 7) code systems may be used. This magnetic flux change is read out as a peak 33a of a reproducing signal 33 (see FIG. 1C) from a magnetic head 32. To decide the phase of the peak 33a, the reproducing signal 33b equalized by an equalization circuit 34 (see FIG. 1D) is differentiated by a differentiation circuit 35. The zero-cross points of the differentiated signal waveform 33c (see FIG. 1E) are converted into a peak pulse train 37 by a pulse forming circuit 36 to thereby detect the phase of the signal peak 33a. A peak detection circuit 38 compares the phase of the detected peak pulse 37 (see FIG. 1F) with a detection window signal 37a (see FIG. 1G) having pulses respectively representing the width of a recording bit and judges by the presence and absence of pulses in the windows whether a bit of the reproducing coded signal 39 (see FIG. 1H) is to be "1" or to be "0". Recently, the pulse width of the window signal 37a generated by an oscillator (OSC) 29 on the basis of the signal 37 has been shortened to 18-19 ns.
In the following, detection error which occurs in the aforementioned peak detection systems is described with reference to FIGS. 2A through 2D as a part of the present invention.
As shown in FIG. 2A, the amplitude of a signal is reduced by the presence of adjacent magnetic flux change 40, that is, intersymbol interference (ISI) and nonlinear distortion occurs. As a result, the phase of a waveform peak 42 shifts by a pattern peak shift value 47 from an ideal isolated reproducing signal waveform When noise is superimposed on this signal, the peak 42 shifts further so that it may be out of a window width 43. In this case, a peak pulse 37 (see FIG. 1F) corresponding to the phase of the peak 42 also shifts toward an adjacent window width 44, so that detection error 46 in two bits of the target window width 43 and the adjacent window width 44 may be brought by bit inversion 45.